Lymphocyte contamination detection

I need to detect if there is a contamination of lymphocytes or other
hematopoietic cells in a culture of primary thyreocytes, and I have to
do by RT-PCR. Does anyone know a good markers? I was thinking to
detect the mRNA of CD45 or other more suitable molecule. The primers
sequence will be very appreciate.
Thank you for the help.
Giuseppe Pizzolanti
Univ. of Palermo, Italy